1 #include<iostream>
2 #include<cstdio>
3 #include<cstring>
4 #include<limits>
5 #include<vector>
6 using namespace std;
7 const int maxn = 10;
8 struct edge{
9 int to, cost;
10 edge(int t){
11 this->to = t; this->cost = 0;
12 }
13 };
14 void addEdge(vector<edge> &edgelist, vector<vector<int> > &G, int from, int to){
15 edgelist.push_back(edge(to));
16 G[from].push_back(edgelist.size()-1);
17 }
18 void addDoubleEdge(vector<edge> &edgelist, vector<vector<int> > &G, int from, int to){
19 addEdge(edgelist,G,from,to);
20 addEdge(edgelist,G,to,from);
21 }
22 bool isCyclic(vector<edge> edgelist, vector<vector<int> > G,vector<bool> vis, vector<bool> RecStack, int v){
23 for(int i=0;i<G[v].size();++i){
24 edge e = edgelist[G[v][i]];
25 if(RecStack[e.to]) return true;
26 if(!vis[e.to]){
27 vis[e.to] = true; RecStack[e.to] = true;
28 if(isCyclic(edgelist,G,vis,RecStack,e.to)) return true;
29 RecStack[e.to] = false;
30 }
31 }
32 return false;
33 }
34 void buildMap(vector<edge> &edgelist, vector<vector<int> > &G){
35 addEdge(edgelist,G,0,1);
36 addEdge(edgelist,G,0,2);
37 addEdge(edgelist,G,2,0);
38 addEdge(edgelist,G,1,2);
39 addEdge(edgelist,G,2,3);
40 addEdge(edgelist,G,3,3);
41 }
42 int main(){
43 vector<edge> edgelist;
44 vector<vector<int> > G(maxn);
45 vector<bool> vis(maxn);
46 vector<bool> RecStack(maxn);
47
48 buildMap(edgelist,G);
49
50 for(int i=0;i<vis.size();++i) vis[i]=false;
51 for(int i=0;i<RecStack.size();++i) RecStack[i]=false;
52
53 for(int i=0;i<G.size();++i){
54 if(!vis[i]){
55 vis[i] = true; RecStack[i] = true;
56 if(isCyclic(edgelist,G,vis,RecStack,i)){
57 cout<<i<<" starts a cycle"<<endl;
58 }
59 RecStack[i] = false;
60 }
61 }
62
63 return 0;
64 }
